Capillary electrophoresis (CE) coupled with mass spectrometry (MS) has been well recognized as a complementary analytical technology to more conventional liquid chromatography-mass spectrometry (LC-MS). By combining the high resolving power of CE with the highly sensitive and information-rich detection of MS, this hyphenated technique has enjoyed successful applications in many fields of scientific research, such as biomarker discovery and verification, metabolomics, identification and quantification of environmental pollutants, and food quality control. Although much less widely applied than LC-MS, the number of publications related to development and application of CE-MS continues to increase because of its potential capability in performing sensitive and high-throughput sample analysis.
The major limitation to the broad applications of CE separation technique is its very limited sample loading capacity as compared to LC-based separation techniques. To overcome this limitation, alternative CE operation modes, such as a combination of capillary isotachophoresis (CITP) and capillary zone electrophoresis (CZE), also called transient isotachophoresis (tITP), were developed to increase the sample loading volume. A typical CITP/CZE separation can be performed efficiently with initial sample loading volume equal to ⅓ of the total separation capillary volume in the range of μL as compared to nL sample loading in traditional capillary zone electrophoresis (CZE) separation. In addition, CITP/CZE separation concentrates or focuses low abundance analytes to a much greater extent than the major components in a mixture, providing a selective enrichment of trace analytes. These two unique features of CITP/CZE—large sample loading volume and analyte focusing—have been explored extensively. CITP/CZE coupled with high sensitivity electrospray ionization mass spectrometry (ESI-MS) was recently shown to significantly improve the limit of detection in quantifying targeted peptides in complex biomatrix. It is highly possible that CITP/CZE-MS can outperform the conventional LC-MS in both sensitivity and separation efficiency if the operation of CITP/CZE-MS can be fully optimized, allowing the CITP/CZE sample loading volume to be comparable to that of LC.
What is needed is a robust interface that effectively couples CE with ESI-MS to allow large sample loading volume and stable ESI for highly sensitive CE-MS analysis.